rii PREFACE 



the book could be built. With this idea as a basis it will readily be 

 seen that a topic might be developed along physical, chemical, 

 biological, geographical and other lines a result which at once calls 

 into play a great variety of facts and experiences which have, 

 nevertheless, a common basis in the home. The author soon discovered 

 that in progressing from one part of the house to another it was 

 necessary that certain fundamental facts be discussed and digested 

 before taking up others; that is, a certain logical progress of devel- 

 opment must in all cases be maintained. Furthermore, it will be 

 found that the sequence of chapters is such that the thought devel- 

 oped in each leads easily and logically into the subject of the fol- 

 lowing. For example, on page 323, Chapter IX, will be found a 

 treatment of germs and disease which concludes with a discussion of 

 germicides and a statement that light is the most powerful of all 

 germicides. The following chapter takes up the subject of Light. 



The teacher will find that some lessons have been planned to 

 develop interest whereas others are essentially fact lessons. Also, 

 he will find numerous questions based upon these two types. More- 

 over, the author has endeavored so to frame questions that they 

 will develop free and informal discussion among the members of the 

 class. In his classes students are given ten minutes of each period 

 within which to bring in their observations regarding phenomena 

 and to give explanations for such phenomena. It is a curious fact 

 that from year to year many of the same observations and questions 

 have been made and asked by different classes. A good plan is to 

 let one student perform the experiment while the whole class enter 

 into the discussion. Definite assignments to students who are espe- 

 cially interested in certain phases of the subject such as the explan- 

 ation of wireless apparatus, etc. are always instructive and worth 

 while provided a general discussion follows the report upon these 

 assignments. The teacher will do well to encourage his students 

 to start interesting discussions by their making statements some- 

 what after this manner: " This morning while coming to school I 

 observed that smoke was sinking toward the ground. I do not 

 know the reason for this but would like to have it explained," or a 

 girl student might say, " Last evening while helping mother wash 

 the dishes I noticed that two of the glasses stuck together. What 



